In the prior art, the conventional engine valve drive technology for the engine ignition is well known and its application has a history of more than one hundred years. However, for the additional requirements on engine emissions and engine braking, more and more engines need different valve motions than conventional valve motions, such as exhaust gas recirculation valve motions that reduce emissions, variable valve motions that increase fuel efficiency (including cylinder cutout with valve motions of zero lift) and engine braking valve motions that slow down the vehicle.
In order to obtain the variable valve motion, for example, from the conventional valve motion to the engine brake valve motion, people often need to add an auxiliary valve drive mechanism (VDM for short) to the conventional VDM, such as a top-mounted brake housing or an integrated brake rocker arm, etc. The structure and control are very complicated, and most of them open the engine valves by hydraulic loading.
The common variable valve motion is a lost-motion type. By changing the linkage between the cam and the valve, some or all of the cam motion is lost and cannot be transmitted to the valve, resulting in reduction or even complete elimination of the valve motion (cylinder cutout). Obviously, the valve motion of the lost-motion type will not completely follow the motion of the cam, and the seating velocity of the valve cannot be controlled by the cam.
The linkage between the cam and the valve can be roughly divided into the fixed chain type and the hydraulic type. Most of VDMs for conventional engine ignition are fixed chain type, with cam direct driving the valve or forming a fixed chain type VDM with solid-to-solid contact through rigid connectors such as a rocker arm (or a push rod and a valve bridge). The cam of the hydraulic variable valve drive mechanism (VVDM for short) is hydraulically linked to the valve, and a (built-in) valve catch (a valve seating mechanism) needs to be provided between the cam and the valve to control the seating velocity of the valve when motion is lost to avoid impact inside the drive mechanism.
For the fixed chain VVDM, there will also be times when the valve motion does not follow the cam motion, such as falling off inside the drive mechanism and valve no-following (bouncing back), which will cause the valve seating velocity to be out of control. Unfortunately, the valve seating mechanism for the hydraulic VVDM cannot be applied to the fixed chain VDM.
The applicant disclosed an engine VVDM by shifting roller in his invention patent application (authorized publication number CN 1043146333 B) on Oct. 15, 2014. The roller drive mechanism shifts the cam roller between the first axial position and the second axial position on the roller shaft through a roller fork, so that the cam roller is connected with different cams and different engine valve events are generated. The roller drive mechanism comprises a piston and a spring, the piston is connected with one end of the roller fork, the other end of the roller fork is provided with two separated guide holes, the two separated guide holes are sleeved on the roller shaft and clamp the cam roller in the middle, and the movement of the piston is transmitted to the cam roller through the roller fork. The engine VVDM from shifting roller can be used for engine cylinder cutout, engine braking, engine exhaust gas recirculation, engine starting and closing, etc.
The above-mentioned fixed chain VVDM by shifting roller still faces two problems. The first is that the roller drive mechanism drives the roller through the roller fork, which is complicated in structure and installation, and the roller fork will generate asymmetric offset load on the roller. The other is that since the brake oil feeding (and brake oil discharging) from the brake oil feed valve is random and not timed (the brake oil feed valve is turned on randomly and the oil can flow to the roller driver at any position/phase of the cam), when the roller moves from one axial position to another axial position on the roller shaft, it is possible to create a transition across two cams of different heights (one cam is in the high position and the other cam is in the low position, rather than two cams are at the same height), resulting in falling off and impact of the roller from the high cam to the low cam.